1. Field of the Invention
The present invention relates generally to improved methods of preparing and using stable oil external-aqueous internal emulsions in oil field applications.
2. Description of the Prior Art
In the stimulation of oil and gas production from a subterranean formation penetrated by a well bore, one heretofore commonly utilized technique is to contact the formation with an aqueous acid solution whereby the acid solution reacts with materials in the formation to form enlarged flow channels therein.
When such acidizing procedures are carried out in formations having naturally low permeabilities, the acid must be delivered deeply into the formation before it spends in order to increase the hydrocarbon productivity of the formation. That is, the increase in the hydrocarbon productivity of a low permeability formation is proportional to the enlargement of the flow channels and distance from the well bore to which acid etching of the formation occurs.
Various techniques have heretofore been developed for retarding the rate at which the acid spends itself in a formation and thereby causing live acid to be delivered into the formation at greater distances from the well bore. The techniques include retarding an aqueous acid solution by forming an oil external-aqueous acid internal emulsion therewith. Such an emulsion has a relatively high viscosity which prevents rapid fluid loss and diffusion of the acid into the formation, and because the emulsion is oil external, i.e., the oil is the continuous phase in which the aqueous acid is dispersed, the spending of the acid on formation materials is retarded whereby deep penetration into the formation with live acid can be accomplished. As the acid in the emulsion contacts and reacts with materials in the formation the emulsion is broken.
High viscosity oil external-aqueous internal emulsions have also been prepared from brines and utilized in oil field applications as diverting agents. That is, a relatively high viscosity oil external-aqueous internal emulsion has been prepared and placed into high permeability zones in subterranean formations such as fractures, thief zones, vugs and the like. The high viscosity emulsion functions to plug the high permeability zones whereby fluids subsequently injected or produced from the formations are diverted away from such zones.
While oil external-aqueous internal emulsions have been successfully prepared and utilized heretofore in the above and other oil field applications, a problem associated with such emulsions is their difficulty of preparation. That is, the preparation of such emulsions has heretofore required high shear batch mixing for relatively long periods of time on the surface prior to introduction of the emulsions into wells. Such surface batch mixing is both time consuming and expensive, particularly where large volumes of the emulsion are required. Thus, there is a need for improved methods of preparing and using oil external-aqueous internal emulsions whereby the emulsions can be rapidly prepared, preferably continuously.